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Gas Shut Off Valve

Freezing Valves?

Today, dealing with cryogenic temperatures is a common task for a fluid system designer. Many common fluids used in propulsion, including liquid oxygen and liquid nitrogen, fall under this category. While the principles behind the control of these fluids remain largely the same as for milder fluids, cryogenics present a unique series of problems to the system designer.

It is well known in the engineering profession that as temperature increases, materials tend to expand. The inverse is also true: as temperature decreases, most materials shrink. This can present a plethora of problems to fluid system and component designers. The most common problem in cryogenic fluid devices is leakage. The elastomeric materials typically used as seals have a much larger coefficient of thermal expansion than the other materials present in the valve. This causes the elastomers to shrink much faster than the valve geometry which surrounds them.

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How a Regulator Works

Pressure regulators are ubiquitous in modern fluid system designs. They allow a system to contain fluid at a much higher pressure (and density, for compressible pneumatic fluids) than the main component’s operating pressures, which ultimately leads to higher energy density in storable fluid systems. Just how does a regulator accomplish this? Read on to find out.

A pressure regulator is a rather simple example of a mechanical closed loop feedback system. By sensing, or ‘reading,’ the pressure at its outlet, the components of the regulator will automatically adjust the position of the poppet to control the flow of fluid through the valve. This is commonly accomplished through the use of surfaces on the poppet which enact a force on the poppet, which is balanced by a spring or controlled pressure volume. When the outlet pressure of the valve produces a force which is equal to the balancing or reference force, the poppet contacts the seat of the valve and the regulator reaches a stage known as ‘lockup.’ Since the poppet’s seating surface is in contact with the valve seat, no fluid can flow through the valve. The outlet of the valve will then remain at constant pressure until the other components of the fluid system cause a change in pressure downstream.

Read more: How a Regulator Works